National Institute for Occupational Safety and Health

SEC-00236 Metals and Controls Corporation

Thorium and Welding Exposure Model 

Christine Corwin

Health Physicist

Teleconference of the Metals and Controls Work Group

January 9, 2020
Background

 The National Institute for Occupational Safety and Health (NIOSH) 

presented the Evaluation Report (ER) for SEC-00236, Metals and Controls 

Corp. (M&C) to the Advisory Board on Radiation and Worker Health on 

August 24, 2017. 

 A petitioner raised a concern about the adequacy of the Evaluation Report 

(ER) in addressing maintenance-type work. 

 In response to this concern, on September 5, 2017, NIOSH initiated 

strategies to continue M&C research and further develop SEC-00236.

– Review monitoring records in the Site Research Database (SRDB) 

– Conduct interviews with M&C workers
Interviews

 From October 24, 2017, through October 26, 2017, NIOSH, Oak Ridge 

Associated Universities (ORAU), and Sanford Cohen & Associates (SC&A) 

personnel interviewed 12 former M&C workers and individuals 

knowledgeable about maintenance work. Interviewers asked questions 

regarding the frequency and duration of work, including heating, 

ventilation, and air conditioning (HVAC), utility and drain line 

maintenance, and new equipment installations. 
Additional Actions

 November 8, 2017 – The Metals and Controls Working Group (Working 

Group), SC&A, NIOSH, and ORAU team members held a teleconference to 

discuss technical issues associated with developing exposure models 

regarding maintenance work. 

 February 6, 2018 – NIOSH obtained additional monitoring data regarding 

remediation work performed by Creative Pollutions Solutions (CPS) in 

1992 and 1994.

 February 13, 2018 - NIOSH received a report by SC&A titled Review of SEC 

Petition ER SEC-00236 (Mauro, 2018). 
Additional Actions (continued-1)

 April 23, 2018 – NIOSH issued the Metals and Controls Corp. Subsurface 

Exposure Model white paper (NIOSH, 2018a) and made it available to 

SC&A and the Working Group. 

 May 3, 2018 - During a Working Group meeting, SC&A presented their 

findings and observations associated with the SEC-00236 ER. The 

petitioners also made a statement and provided a letter with their 

concerns. After the meeting, an issues matrix was created. 

 August 22, 2018 - During a full Advisory Board meeting, the Working 

Group presented their findings and observations associated with the SEC00236 ER and NIOSH provided an update. The petitioners also made a 

statement and provided a letter with their concerns. 
Additional Actions (continued-2)

 November 20, 2018 – During a Working Group meeting, NIOSH presented 

the Metals and Controls Corp. Maintenance Exposure Model white paper 

(NIOSH, 2018b) that included HVAC maintenance and Building 10 

overhead exposure models. SC&A presented their observations associated 

with the Metals and Controls Corp. Subsurface Exposure Model and Metals 

and Controls Corp. Maintenance Exposure Model white papers.

 December 13, 2018 - During a full Advisory Board meeting, the Working 

Group presented an update. The petitioners also made a statement and 

provided a letter with their concerns. 
Additional Actions (continued-3)

 April 8, 2019 – NIOSH issued the Metals and Controls Corp. Thorium and 

Welding Exposure Model white paper (NIOSH, 2019a) and made it 

available to SC&A and the Working Group. 

 July 26, 2019 – NIOSH received an 8-page memo by SC&A titled Review of 

NIOSH’s “Metals and Controls Corp. Thorium and Welding Exposure 

Model” (SC&A, 2019). 
Recent Petitioner Concerns

 The Metals and Control Corp. Thorium and Welding Exposure Model white 

paper addresses two concerns raised by the petitioner (Elliott, 2018):

– Exposures to thorium that occurred while working inside Building 10 

– Exposures that occurred during welding activities
Internal Exposures to Thorium

 Petitioner Issue: The 1995 Drainage System Characterization Report 

(Weston, 1996) included 15 grab samples of accumulated sediment or 

surrounding soils in discrete locations of the pipe where elevated direct 

measurements were observed. The grab sample analyses reported an 

isotopic analysis of uranium but no other radionuclides. In retrospect, we 

now know that thorium would have also been present, as it was 

historically processed on the same manufacturing equipment as uranium 

during the Atomic Weapons Employer program. But given the limitation of 

the 1995 survey measurements, we have no way of knowing how much 

thorium source term was present in the residual radioactivity to which the 

M&C maintenance workers were exposed (Elliott, 2018).
Internal Exposures to Thorium (continued-1)

 Thorium Operations

– During AWE operations, thorium-bearing component fabrication 

occurred (including reactor fuel, metallic alloys, and metallic foils).

– The only definitive information regarding the amount of thorium at 

M&C is from a 1962 nuclear safety analysis that listed the total 

quantity of thorium as 244 kg.

– There was approximately 32 times as much uranium as there was 

thorium-232 in the 1962 inventory data.

– The activity ratio showed there was 188 times more uranium 

(assuming natural uranium and thorium-232).
Internal Exposures to Thorium (continued-2)

– As M&C cleaned the areas used for AWE operations prior to 1968, 

they buried waste and materials in the are between Buildings 11 and 

12.

– In 1984 the U.S. Nuclear Regulatory Commission (NRC) performed 

verification sampling of the burial area.

• Contamination above release limits

• Presence of thorium

– In 1992 CPS performed additional sampling of the burial area and 

corroborated the presence of thorium.
Internal Exposures to Thorium (continued-3)

 New NIOSH Thorium Exposure Bounding Method

– Although M&C only analyzed Building 10 subsurface samples for 

uranium in 1995, NIOSH can bound thorium exposures during 

maintenance work. 

• Assuming that the subsurface sediments contained equivalent 

amounts of natural uranium and thorium-232.

– NIOSH determined the sediment to be about 1% (by weight) natural 

uranium.

• Using the previously determined 95th percentile measured 

uranium activity in the sediment documented in the Metals and 

Controls Corp. Maintenance Exposure Model white paper (NIOSH, 

2018b). 
Internal Exposures to Thorium (continued-4)

– Thorium air concentration of 2.2 μg/m3 

• Subsurface was contaminated with equal amounts of thorium and 

uranium. 

• 1% of the sediment and sludge, and the subsequent dust loading 

created from maintenance work. 

– Air concentration of 2.42 x 10-13 μCi/mL.

• Using the thorium-232 specific activity (0.11 μCi/g),

– Inhalation committed effective dose (CED) of 10.42 mrem/yr. 

– Adding ingestion the estimated dose becomes 14.78 mrem/yr.
Internal Exposures to Thorium Conclusions

– Calculated air concentrations can be used to bound internal thorium 

exposures that occurred while performing subsurface maintenance 

within Building 10.

– For those areas where gross alpha contamination surveys are 

available, NIOSH will continue to estimate worker doses using the 

most claimant-favorable isotope of thorium or uranium.

– For the burial area and Building 10 outside perimeter, NIOSH can use 

isotopic thorium-232 results to model air concentrations breathed by 

maintenance workers as previously described in the Metals and 

Controls Corp. Maintenance Exposure Model white paper (NIOSH, 

2018b).
Internal Exposures from Welding

 Petitioner Issue: Sometimes the roof penetration work also involved 

welding of structural framework. This created a further risk of inhaling 

welding fumes without the benefit of any respirator (Elliott, 2018). 
Internal Exposures from Welding (continued-1)

 Welding Operations

– During the residual period, while performing maintenance work in the 

Building 10 overhead area, M&C workers were potentially exposed to 

contamination remaining from AWE operations: 

• Installing pipe racks;

• Welding supports to the trusses to fortify the roof; 

• Cutting and drilling up through the roof to make penetrations for 

running services to rooftop equipment; 

• Installing equipment on the roof. 
Internal Exposures from Welding (continued-2)

– A June 1981 NRC Inspection Report stated that there was a “Cutting 

and Welding Permit” program at M&C.

– The permit system used a card on which the necessary precautions 

required to be taken were listed. 

– The 1964 M&C Safety Manual specified welding and flame-cutting 

precautions for fire safety, including pre-work cleaning of combustible 

debris, removal of deposits inside of ductwork, use of curtains and 

shields to protect personnel from glare and sparks, and use of “permit 

required” areas for sewers, pits, drains, ventilators, and ducts. 

– The Safety Manual also stated that barricades were required for 

overhead work (M&C Nuclear, 1964). 
Internal Exposures from Welding (continued-3)

 NIOSH Welding Exposure Bounding Method

– Interviews of M&C maintenance personnel indicated that welding in 

the dusty overhead area of Building 10 was only one of their many 

duties, and occupied approximately 4 hours per month, or 48 hours 

per year.

– NIOSH previously characterized the overhead work environment using 

the total surface activity, and assumed 10% of that activity was 

removable and available to generate airborne activity. NIOSH will 

continue to assign doses using this method for other work in the 

overhead area (e.g., light bulb replacements); however, for welding, 

NIOSH will assume 100% of the activity is resuspended.
Internal Exposures from Welding (continued-4)

– NIOSH previously modeled exposures for the entire overhead area 

uniformly using the 95thpercentile contamination level and a 1 x 10-4

resuspension factor. 

• Good work practice requires clean bare metal prior to welding, 

which can include wire brushing and grinding as described in 

worker interviews and can generate the highest airborne 

concentrations.

• NUREG-1400 (NRC, 1993) Section 1.2.3 indicates that a 

dispersibility factor of 10 should be used when modeling intakes 

that involve grinding operations. 
Internal Exposures from Welding (continued-5)

– NIOSH will increase the resuspension factor and apply a value of 1 x 

10-3 to the 95thpercentile contamination level.

– This air concentration would be assumed to be inhaled for the 48 

hours of welding that occurred per year for M&C personnel that 

performed welding in the Building 10 overhead area.

– Using this information NIOSH determined an air concentration of 4.05 

x 10-12 μCi/mL.

• Inhalation CED of 16.75 mrem/year. 

• Estimated dose with ingestion is 16.77 mrem/year.
Internal Exposures from Welding Conclusions

 NIOSH will assume 100% of the total surface activity is removable and 

available for resuspension.

 NIOSH will increase the resuspension factor and apply a value of 1 x 10-3 to 

the 95th percentile contamination level.

 This air concentration will be assume to be inhaled for 48 hours of welding 

each year and will be assigned in addition to other assigned exposures.
References

 Elliott, 2018, Special Exposure Cohort Petition SEC00236, correspondence 

to National Institute for Occupational Safety and Health; Michael J. Elliott; 

May 28, 2018. [SRDB Ref ID: 172717] 

 Mauro, 2018, Review of SEC Petition Evaluation Report SEC-00236 Metals 

and Controls Corporation, SCA-TR-2018-SEC001, Revision 0; John Mauro, 

Robert Anigstein, Rose Gogliotti, and Nicole Briggs; February 2018. [SRDB 

Ref ID: 172715] 

 M&C Nuclear, 1964, Health and Safety Manual; 1964. [SRDB Ref ID: 13642]

 NIOSH, 2018a, Metals and Controls Corp. Subsurface Exposure Model; 

April 23, 2018. [SRDB Ref ID: 174132] 
References (continued)

 NIOSH, 2018b, Metals and Controls Corp. Maintenance Exposure Model; 

October 24, 2018. [SRDB Ref ID: 174357] 

 NIOSH, 2019a, Metals and Controls Corp. Thorium and Welding Exposure 

Model, Aril 8, 2019. [SRBD Ref ID: 175938]

 NIOSH, 2019b, NIOSH Response Paper, SC&A Review of Metals and 

Controls Corp. Thorium and Welding Exposure Model; November 27, 

2019. [SRDB Ref ID: 178695]

 NRC, 1993, NUREG-1400 Air Sampling in the Workplace, September 1993. 

[SRDB Ref ID: 20129] 
References (continued)

 SC&A, 2019, Review of NIOSH’s “Metals and Controls Corp. Thorium and 

Welding Exposure Model, July 26, 2019. [SRBD Ref ID 177001]

 Weston, 1996, Texas Instruments Incorporated Attleboro Facility Building 

Interiors Remediation Drainage System Characterization; prepared by Roy 

F. Weston, Inc., January 1996. [SRDB Ref ID: 165965]